1. Field of the Invention
The present invention relates to inhalation/breath actuated devices for use with metered dose inhalers (MDIs). Metered dose inhalers, as used herein and as commonly used in the art, are comprised of an aerosol canister which contains medicament for administration to the lungs, a metering valve which is disposed in the canister and which releases a predetermined amount of medicament from the canister when the canister is actuated, an actuator which holds the canister and includes a opening for oral inhalation, and an actuator stem which channels the medicament released by the metering valve out through the opening and toward the user. More particularly, the present invention relates to a device which receives a metered dose inhaler and which automatically actuates the metered dose inhaler responsive to inhalation by the user.
2. State of the Art
When an asthmatic or other person suffering from inhalation problems has difficulty breathing, it is typically desirable to introduce medicament into the person""s lungs to restore normal breathing patterns to the extent possible. For many years, this has been accomplished by the use of metered dose inhalers. The metered dose inhalers include a canister which contains medicament and a propellant, a metering valve which dispenses the medicament from the canister, an actuator body that receives the canister and which forms an opening for oral inhalation, and an actuator stem which receives medicament from the canister and directs it out the opening in the actuator body. Moving the medicament canister relative to the actuator body and actuator stem causes the metering valve to release the predetermined amount of medicament. Each metered dose inhalator is regulated by the U.S. Food and Drug Administration and each of the components is specifically designed relative to the parameters of the other components.
When the user is having difficulty breathing, the opening of the actuator body is placed in the user""s mouth and then the canister is moved downwardly in the actuator so that the metering valve discharges the predetermined dose of medicament and propellant. The medicament passes through the actuator stem and then out the opening in the actuator body.
One problem which is recurrent in the use of metered dose inhalers is that the user often actuates the metered dose inhaler and then begins inhalation. Such an inhalation/medicating pattern limits the amount of medicament delivered to the lung and causes most of the medicament to impact the mouth and throat. Thus, the user obtains much less than an optimal dose of medicament.
In attempts to overcome the problems associated with manual actuation of the metered dose inhalers, several inhalation/breath actuated metered dose inhalers have been developed. Such devices are designed to provide proper coordination of dispensing a dose of medicament with the inhalation of the user, thus providing for the maximum proportion of the dose of medicament to be deposited in the lungs. Examples of such devices are described in U.S. Pat. Nos. 5,404,871; 5,347,998; 5,284,133; 5,217,004; 5,119,806; 5,060,643; 4,664,107; 4,648,393; 3,789,843; 3,732,864; 3,636,949; 3,598,294; 3,565,070; 3,456,646; 3,456,645; 3,456,644; British Patent Specification Nos. 2,061,116; 1,392,192; 1,335,378; 1,269,554 and German Patent No. 3,040,641.
Existing breath-actuated inhalers are designed to accommodate available aerosol canisters separate from the receiving bodies or housings for which they were originally designed, marketed, and approved by the Food and Drug Administration (FDA). Aerosol medications of the pressurized inhaler type are drug products approved and regulated by the FDA as the combination of the pressurized aerosol canister and the actuator used to atomize the canister metering valve contents. The actuator is regarded as an integral part of the aerosol drug delivery system, since the design of the housing greatly influences the nature of the aerosol spray generated for inhalation by the patient. The design of the actuator impacts not only the amount of medication released from the inhaler, but the amount of medication received by the patient due to the actuator""s influence on the particle size and velocity distribution of the emitted aerosol mist and the influence of the particle or droplet size distribution and velocity on impaction in the patient""s respiratory tract.
As a consequence, existing breath-actuated inhalers must be approved by the FDA in conjunction with a particular aerosol-based medication canister. As a result, these inhalers have not been generally available to the patient public for use with the full range of aerosol-based medications which are available for the treatment and management of disease. For example, a person must obtain a breath actuated device that has been approved by the FDA with the canister of medication recommended by the physician or the individual must obtain a metered dose inhaler of the desired medication, i.e., the combination of the medicament container and the actuator approved by the FDA.
A problem with many of the mechanical breath-activated inhalers is that the aerosol canister remains in the depressed position (after firing by the inhaler""s internal actuation mechanism) until the patient physically intervenes and relieves the mechanical load on the aerosol canister by moving a lever, strap, or some other mechanical means. Immediately after venting, the metering chamber (valve) of the aerosol canister becomes vulnerable to the intrusion of air and the extent of air intrusion increases with the length of time the canister remains in the depressed position. The intrusion of air in this fashion can result in xe2x80x9cvapor lockingxe2x80x9d of the metering valve, resulting in incomplete filling of the metering chamber of the valve when the canister is ultimately released from the depressed position. Incomplete filling of the metering chamber, in turn, results in incomplete dosing on the next actuation of the inhaler, due to the lower quantity of drug which has entered the metering chamber from the liquid contents of the canister.
Another problem associated with some mechanical breath-actuated inhalers is that the aerosol canister actuation mechanism must be in the xe2x80x9carmedxe2x80x9d, ready to fire, position in order to allow recovery of the aerosol canister from the depressed position under the action of it""s own internal valve spring. Two potential consequences may result from this condition. First, the actuation mechanism may be xe2x80x9carmedxe2x80x9d during the intervals between inhaler use or, second and of potentially more seriousness, the actuator mechanism may be xe2x80x9carmedxe2x80x9d during storage. This is particularly concerning when the device, as a consequence of its sale in combination with an aerosol canister as mandated by the FDA, is packaged with an aerosol canister in place. Thus, the actuator mechanism could be in the armed position for up to three years. In either event, the functional life and reliability of the device may be compromised by the long term stress effects of maintaining the actuation mechanism in the xe2x80x9carmedxe2x80x9d position for extended periods.
In addition to the above, the actuator mechanism may xe2x80x9crelaxxe2x80x9d or creep, in either a fluid or bulk mechanical sense, if the device is stored for prolonged periods in the xe2x80x9carmedxe2x80x9d position, resulting in a change in actuator functionality with effects that may range from xe2x80x9cprematurexe2x80x9d firing of the aerosol canister to delayed or extended firing time during the canister depression phase. In both cases the patient does not receive the prescribed dose of medication which the inhaler was designed to deliver.
Electro-mechanical inhalers are also known. U.S. Pat. No. 5,347,998 describes a breath-actuated inhaler with an electromechanical priming mechanism. It is the object of the invention described therein to provide an inhalation device for use with pressurized aerosol canisters which does not require manual priming for firing the valve contained within the aerosol canister. Further, the inhaler provides an electromechanical means for relieving the firing load imposed on the aerosol canister during actuation.
U.S. Pat. No. 5,284,133 describes a dose timer, actuator mechanism, and patient compliance monitoring means. The invention relates to a dose or timing controlled actuator that operates in conjunction with an inhalation device to prevent both patient under-compliance with prescribed medication dosing and patient abuse of or dependence on prescribed medication. The invention contemplates the use of an actuator to prevent patient actuation of the inhalation device at non-prescribed intervals or at higher than prescribed doses, and the use of an alarm to notify the patient regarding undercompliance/underdosing situations and attempted abuse situations.
U.S. Pat. No. 5,404,871 describes an apparatus and method for delivering an amount of aerosolized medicine for inspiration by a patient in response to the occurrence of an appropriate delivery point or points in the patient""s detected breath flow. Changes in a patient""s breath flow pattern during the course of an aerosolized medication inspiration therapy program may be detected and used to adjust the controlled amount of medication to be delivered in a given administration and/or to conform to the pattern of the patient""s condition or change in condition. The device may also contain a library of administration protocols or operating parameters for different medications and means for identifying, from the canister, the medicinal contents of the canister for customizing operation of the apparatus.
U.S. Pat. No. 5,497,764 describes a portable, battery powered, hand-held system for releasing a controlled dose of aerosol medication for inhalation by a patient including a durable body and an aerosol medication cassette inserted in the durable body. The durable body includes an actuator mechanism for engaging an inserted cassette and its canister, and an actuator release mechanism for controlling the actuator mechanism to depress the canister for a selected period of time to release the desired dose of medication and then release the canister. The actuator mechanism, includes a compression spring for depressing the canister and a torsion spring for reloading the compression spring. The torsion spring is reloaded by rotating the cassette from an open position for delivering aerosol to a closed position. The actuator release mechanism includes a motor and trigger in assembly that controls the release of the compression spring and the torsion spring, and, hence, the time that the canister is depressed.
An additional problem with the presently available breath/inhalation actuated metered dose inhalers is the risk which is posed by actuator failure. Because the devices replace the conventional actuator body, many of them have no mechanism which permits manual actuation of the canister in the event the breath/inhalation activated mechanism fails. If a spring or other component of the devices were to fail, the user may have no way to dispense the medicament contained within the canister. Thus, a user may be deprived of medicament while undergoing an asthma attack due to actuator failure.
Thus there is a need for an improved device for use with metered dose inhalers. Such a device should be easy to use and relatively inexpensive. Additionally, such a device should not require replacement if new medication is to be used, and should allow for conventional actuation of the metered dose inhaler when desired.
It is therefore an object of the present invention to provide a novel inhalation device for use with metered dose inhalers (MDIs).
It is another object of the present invention to provide a device for use with metered dose inhalers which dose not require replacement of the device when medicament is changed.
It is another object of the present invention to provide an inhalation device for use with metered dose inhalers which includes a mechanical mechanism for applying the force required to actuate a metered dose inhaler at a preset patient inspiration flow rate.
It is still another object of the invention to provide such a device wherein the metered dose inhaler is physically incorporated into the device with the aerosol canister still housed in the actuator for which the medication has received FDA approval.
It is yet another object of the present invention to provide an auto-return mechanism for returning the aerosol canister of a metered dose inhaler to a xe2x80x9crestingxe2x80x9d position within a brief time following actuation to assure that the metered dose inhaler is properly xe2x80x9cprimedxe2x80x9d for administration of a subsequent dose.
It is a further object of the present invention to provide viscoelastic means for controlling the timing function of the auto-return mechanism.
It is yet a further object of the present invention to provide means for arming the mechanical metered dose inhaler actuation mechanism, just prior to use, by incorporating the arming function with opening of the device for use.
It is still a further object of the present invention to provide a mechanical override mechanism by which the metered dose inhaler may be actuated by the mechanical actuation mechanism without the necessity of the patient achieving the predetermined inspiration flow rate.
It is still a further object of the present invention to provide a dose-counting means associated with the metered dose inhaler actuation to count the number of medicament doses dispensed or available from the aerosol canister.
Still yet another object of the present invention is the provision of a blocking mechanism to prevent premature firing. Preferably, such a mechanism would prevent firing when the mouthpiece is closed and the manual actuation button depressed, or by accidental droppage of the unit with the mouthpiece closed.
Still another object of the present invention is to provide an adaption mechanism to facilitate use of different sizes and styles of FDA approved metered dose inhalers (aerosol canisters and the associated actuator).
The above and other objects of the invention not specifically recited are realized in specific illustrated embodiments of a breath/inhalation actuated device for use with metered dose inhalers including a housing having a cavity formed therein which is configured for receiving the aerosol canister and the actuator body of a metered dose inhaler and holding the metered dose inhaler in communication with an opening in the housing for dispensing medicament therethrough from the metered dose inhaler. The device also includes a mechanism for automatically activating the metered dose inhaler in response to inhalation of a user through the opening to vent the aerosol canister and provide medicament to the user.
In accordance with one aspect of the invention, the device also includes a return mechanism for automatically deactivating a vented metered dose inhaler to its unvented position where medicament is no longer dispensed therefrom. Preferably, the return mechanism acts in response to the activating means.
In accordance with another aspect of the invention, the housing comprises a cap covering the opening when the cap is in a closed position and exposing the opening when the cap is in an open position. The cap is moveable from its closed position to its opened position in such a manner as to arm the means for depressing the metered dose inhaler.
In accordance with yet another aspect of the present invention, the device further includes a control mechanism for controlling the time of venting of a metered dose inhaler. In a preferred embodiment, the control mechanism includes a mechanism which returns the aerosol canister to the unvented position, and a deformable viscoelastic element which creates a delay for increasing the amount of time the aerosol canister is in the unvented position.